The present invention relates to temperature sensing and indicating apparatus, and more particularly to devices for indicating deviations from a predetermined, normal temperature at a steam trap or other device designed to operate at a substantially constant temperature. Such devices can employ temperature responsive means, for example bimetallic elements, to continually and substantially instantaneously respond to changes in temperature.
A typical steam trap is a pipe coupled automatic valve that permits condensate (condensed steam) to pass, but is a barrier to steam in vapor form. Failure of a steam trap in its open position causes substantial waste of energy, undue pressurization and excessively high temperature in condensate systems, reducing efficiency. Failure with the steam trap closed, due to mechanical failure or accumulation of dirt, scale or other residue, prevents efficient heat transfer and can result in the formation of carbonic acid, which can corrode the steam system. Failure also can occur at a position intermediate the open and closed positions.
In any event, a defective steam trap can be detected by monitoring temperatures at selected locations during system operation. In particular, temperature sensitive devices operative over ranges encountered in the steam system can be place at the steam trap inlet and outlet, and their indications of temperature observed.
A variety of temperature sensing approaches are known, including contact stethoscope devices, chemical sensors which undergo visual changes responsive to temperature, pyrometric measuring devices, infrared emission detecting devices, pressure gauges, surface thermometers, and even the intermittent opening or venting to the atmosphere of valves in condensate discharge lines for direct visual inspection. Infrared emission sensors are accurate but quite expensive. Other visual devices also tend to be expensive and are subject to erroneous readings. Pyrometric and pipe surface thermometer measurements provide information that is sufficiently accurate but can be cumbersome to use.
U.S. Pat. No. 4,575,258, issued Mar. 11, 1986 to the inventor herein, discloses a curved bi-metallic strip mounted to the exterior surface of a steam pipe, and having a free end on which is mounted a rotatable dial. A rod attached at one end to the bi-metallic strip and at the other end to the dial, rotates the dial in response to flexure of the bi-metallic strip as it experiences changes in temperature. While this device clearly indicates temperature deviations, and at relatively low cost, there has remained the need for a simpler, less costly and more reliable steam trap failure indicator, and for an indicator capable of retaining the indication of a maximum temperature deviation over a selected period of time.
It therefore is an object of the present invention to provide a low-cost, reliable temperature detecting apparatus for providing a clear indication of deviations from a standard or normal temperature, and which can be employed with typically encountered pipe surfaces in steam systems.
It is another object of the invention to provide a failure detection apparatus including a thermally sensitive strip which substantially conforms to the surface of the structure being monitored.
Yet another object of the invention is to provide an apparatus that indicates temperature deviations based principally upon linear movement of an indexing member.
It is another object of the invention to provide an apparatus for relatively permanently indicating the maximum deviation from a standard temperature over a selected time period.